This is the VOA Special English Agriculture Report.

Companion planting is the idea that when some crops are planted together, they help each other grow. These compatible plants generally have similar needs for nutrients, soil and moisture.

Advice for companion plantings is sometimes based more on tradition than proof. But Fabian Fernandez at the University of Illinois says there is evidence for some combinations. These can lead to better crops, reduce disease and help with pest control by attracting helpful insects.

For example, some kinds of soil bacteria take nitrogen from the air and make a form that plants can use. The plants keep the nitrogen in their roots. Legumes are especially good at this. Any crops sharing the same space can get the nitrogen as the roots decompose.

Crops like beans and potatoes can also share territory well because their roots reach different levels in the soil. Deep-rooted vegetables get nutrients and moisture from lower down, so they do not compete with shallower plants.

But some plants placed together may harm each other's development.

For example, tomatoes do not like wet soil but watercress does, as the name suggests. So you would probably not want to put them together.

Even after harvest, some kinds of produce should be kept apart. Apples, for example, release ethylene gas, a plant hormone. It can cause other foods to ripen too quickly. Fruits that release a lot of ethylene also include apricots, melons and tomatoes. Vegetables easily affected by ethylene include asparagus, broccoli, cabbage and cucumbers.

Markets often separate high ethylene-producing foods from those that are sensitive to the gas. But sometimes you might want them together. For example, if you put an apple in a bag with a green banana, the banana will be ready to eat sooner.

Now what about peaches, plums and nectarines that are too firm to eat? Growers in California answer this question at eatcaliforniafruit.com. They say an apple, banana or a riper piece of fruit is not needed. The peaches, plums and nectarines themselves release enough of the gas to ripen successfully.

Their advice: Place the fruit in a fruit bowl or in a paper bag with the top folded over. Keep the fruit at room temperature, out of direct sunlight. When the fruit is soft enough to your liking, either use it or place it in a refrigerator to stop further ripening.

And thats the VOA Special English Agriculture Report, available online at voaspecialenglish.com.